First I want to say thanks to everyone who posted their solutions for this problem.
I ended up having to take an indoor photo of about 30 people in a confined space (an office). They were in about 4 or 5 rows, so I needed a lot of depth of field.
I stood up on a chair and set my camera to manual exposure, ISO 1600, f6.3 at 1/60th. I was using a Canon 5D Mark 2 with the flash mounted on the camera. First I tried using the Gary Fong (which is supposed to “spread the light”) and that didn’t work. Incredibly, what worked was popping up the little white plastic bounce card on the flash and bouncing the light off the ceiling. The photo came out perfectly exposed and everyone is tack sharp from front to back.
Someone gave me the Gary Fong Tupperware a few years ago and I can honestly say that despite trying it many times I have never found it to be anything but useless. The only time it ever came in handy was when I was shooting a photo of some kids who thought it was so funny looking that they ended up laughing and I got great shots. I told them that I keep my snacks in it for when I get hungry.
And yet Gary Fong is a gazillionaire selling all manner of plastic and rubber “light spreaders.”